Does anyone know why there are two oil pressure switches on my '90 L98? Both have three pins on the sensor, but the plastic one only uses the center pin which is for the gauge and the metal one only uses the left and right pins which is for the fuel pump. I want to install the metal one on my LS3 because I have had nothing but trouble in the past with the plastic type. Does anyone know if it will work with the gauge?

Thanks!

 

As you see one is a "switch" while the other is a "sensor".

I'm not sure if a "metal one' would work; can you check the application for said metal one?

 

Maybe one is for the mechanical gauge in you car (assuming its a later C4) and one is for the digital readout... OR since you said it connects to the fuel pump, maybe when your oil pressure is way too low the fuel pump cuts to prevent damage???

Those are my guesses???

 

Guessed wrong
Oil pressure SWITCH operates the fuel pump when oil pressure over 4 psi as back up to fuel pump relay.Does not work as safety device because if OP drops
you still have the pump operating from the relay to keep engine running

3 wire unit is combined OP switch and digital gauge unit
Edit
1 wire unit is for oil warning light I have now been informed

 

So I was semi Correct... What no partial credit for the analog and digital gauges???

 

The OIL PRESSURE SAFETY SWITCH MYTH will not die.

One is for the oil press gage. The other provides a backup power source for the fuel pump. IT DOES NOT SHUT OFF THE FUEL PUMP IN THE EVENT OF LOW OIL PRESSURE!!!

 

No it won't, however the piston rings will eventually shut to engine off for you.

 

The oil pump safety switch serves two purposes. The three wires are (1) power from the ignition, (2) power from the starter solenoid and (3) power to the fuel pump .

The first function is to provide the engine with fuel during start up. When starting the car, there is no oil pressure to close the oil safety switch. Power comes from the energized starter solenoid and is routed through a set of contacts in the oil safety switch to the fuel pump, allowing the pump to operate while the starter is turning the engine over.

When the engine first starts, the driver releases the ignition key and the starter solenoid is de-energized. At that point the fuel pump is no longer receiving power from thr starter solenoid. But by now oil pressure has begun to build and oil pressure then closes the ignition to fuel pump contact, providing the normal source of power to the pump while the engine is running.

The second function is to protect against fire. The "safety" part of the oil safety switch is not so much to protect the engine against damage from low oil pressure. The real safety function occurs in the advent of an accident, where the engine has stopped, but driver has not turned the ignition off or is unable to do so. A lack off oil pressure then causes the oil safety switch to then open, cutting off power to the fuel pump. This eliminates a fire hazard from a fuel pump that could otherwise continue to run.

 

`
My God! That whole post is a figment of your imagination. Incredible!

Tell me more about this "oil pump safety switch."

Where in the Cornbread Hell did you come up with this?

 

Was always told they had good drugs out in Ca
Where do you see a connection to the starter solenoid?
Actually , where do you see a connection to Ign , because OP switch is fed direct from battery via a fusible link



So what cuts off the fuel pump relay which runs in parallel to the oil pressure switch ????
Taking the switch out doesn't stop pump running

 

I think Mr. Woolford is correct.

 

in my experience with them so far, their purpose is to leak oil down the back of the block and onto the cats. this causes you to replace the intake seals and the distributer seal while it was them leaking the whole time. oh well, at least i have some new seals and was really able to clean everything well while i had it all apart!

 

some of you others have to learn basic 12 volt DC it seems................

 

You must be smoking the same stuff.

 

Mea Culpa.

First a little history. In a time long ago, all fuel pumps were mechanical and if the engine quit turning, the fuel flow quit. Simple. Foolproof.

Then someone got the idea to put an electric motor inside the gas tank. This great idea was called an in-tank fuel pump and was adopted industry wide (although some electric pumps were mounted outside the tank).

But wait, the pump can't always run just because the ignition key is on; especially in the advent of an accident. To protect against this an oil pressure activated switch was installed in the elecrical feed to the electric fuel pump. Hence the "oil pressure safety switch".

I assure you that at that state of developement, the operation and wiring as I described it was correct.

However time marches on. What was simple, became complex. And yes, the applicable schematic is exactly as posted above by JROD is absolutely correct.

My apologies to anyone and everyone on this forum for posting outdated or inaccurate information.

My special apology to JROD who was offended to the point that he felt the need to bolster the strength of his argument with libel and character assasination.

Or, as Mr. T would say, " I pity the fool....".

 

In reading the posts prior to your posting , did you not at least question the validity of your assumption or do a little background research?
A search would have bought up the numerous posts as to the fuel safety cut off switch
Another quote ,
" tis better to appear a fool than open one's mouth and remove all doubt"

 

At least when he is wrong, he doesn't fool around.